Windows User Authentication error 1219 (WNetUseConnectionW)

Error

When you save the Windows User Authentication settings in a backup set, you see:

[WNetUseConnectionW] (1219) Multiple connections to a server or shared resource by the same user, using more than one user name, are not allowed. Disconnect all previous connections to the server or shared resource and try again.

This is a Windows error, not a fault in the backup client. It normally happens when the backup set reads from a UNC path on a file server or NAS.

Cause

Windows allows only one set of credentials per server name in each logon session. If the logged-on user already has a session open to the server, for example a mapped drive or an open UNC path, under different credentials from the ones entered in the backup client, Windows blocks the second connection.

Fix

Both options below work. Option 1 leaves the user’s mapped drives in place, so try it first.

Option 1: Use a different name for the server (keeps mapped drives)

Windows treats each name for a server as a separate server. Give the backup client its own session by addressing the server another way:

1. In the Domain Name / Host Name field, enter the server’s IP address or fully qualified name (e.g. SERVER.yourdomain.local) instead of the short name.
2. Change the backup source path to match, e.g. \\192.168.1.10\share or \\SERVER.yourdomain.local\share. If the source still uses the short name, the conflict returns.
3. Save the backup set.

Option 2: Remove the existing session

1. Open Command Prompt as the logged-on user and run net use
2. Delete each entry pointing at the server, using the name shown, e.g. net use X: /delete, net use \\SERVER\share /delete or net use \\SERVER\IPC$ /delete
3. Open Credential Manager › Windows Credentials and remove any saved entry for the server under a different account.
4. Save the Windows User Authentication settings again.

net use * /delete /y clears every connection at once, but it also disconnects all mapped drives.

Notes

• If the account is a domain account, enter the domain name in the Domain Name / Host Name field rather than the server name.
• Windows User Authentication is only needed when the backup set reads from network shares. If the client is installed on the server and backs up that server’s own local drives, you can switch it off.
• Scheduled backups run under the backup service, so they may succeed while the setting can’t be saved from the logged-on session. Apply the fix anyway, so the source and credentials stay consistent.

See also: Backup source does not exist!

Applies to: Server and Desktop software on Windows.